Charged particle beam systems are used in a variety of applications, including the manufacturing, repair, and inspection of miniature devices, such as integrated circuits, magnetic recording heads, and photolithography masks. Dual-beam systems typically include a scanning electron microscope (SEM) that can provide a high-resolution image with minimal damage to the target, and an ion beam system such as a focused or shaped beam system, that can be used to alter substrates (e.g., by milling) and to form images.
Generally, the final lens of an SEM produces a magnetic field which can alter the trajectory of the ion beam and can also interfere with various other functions of the dual-beam system. For example, an image or information about the composition of the substrate can be obtained by collecting secondary particles ejected as the primary ion beam strikes target, however, the magnetic field of the SEM changes the path of the secondary particles and makes them difficult to collect. Typically, the solution to this problem is to turn off the SEM when using the ion beam or when using certain functions of the ion beam.
Focused ion beams (FIBs) mill by sputtering, that is, physically removing atoms and molecules from the substrate surface. FIB systems generally operate by directing a focused beam of ions over the surface of a substrate, typically in a raster pattern. The ions are typically extracted from a liquid metal ion source (LMIS) or a plasma source. The extracted ions are accelerated and focused onto the substrate using a series of apertures and electrostatic lenses.
When using FIBs, it is desirable that the beam be free of impurities that can potentially damage the substrate. Accordingly, there is a continuing need for improved dual beam systems.